Design and Analysis of a Generic Fixture for Physical Squeak and Rattle Prediction

Sammanfattning: The thesis work investigates the possibility of replacing the Body-In-White (BIW) sections used in a physical test with a fixture. Volvo-cars perform several sub-system tests on its car components taken from various car models for different issues. Squeak and Rattle in Cockpits is one such important phenomenon investigated through its sub-system tests. Currently, the Body-in-White (BIW) sections taken from car body are used in holding the cockpits for Squeak and Rattle physical testing on a vibrating rig, the idea is to design a fixture that can replace these BIW sections for the test. Additionally, it is ensured that the fixture is designed to accommodate a variety of cockpits through the flexibility in its structure. Models from two different car segments were considered for performing the thesis. The development process started by researching the theory behind squeak and rattle along with investigating the important design parameters which would determine the requirements on the fixture. This is followed up with benchmarking the parameters and a physical test which would help later in comparison and evaluation of fixture performance against the BIW. The result from benchmarking were then used for topology optimization in obtaining a material layout to provide a basis for fixture design. Then, a basic CAD model is generated which is adapted to provide flexibility using Aluflexmechanisms. The final design comprises of a sufficiently rigid main structure made of hollow steel beams upon which Aluflex mechanisms are attached to provide flexibility in accommodating a variety of cockpit models. The fixture is analyzed and evaluated by comparing with benchmarked data. With the thesis, a fixture with generic (flexible) features which is manufacturable has been designed. It was concluded that at its current stage it cannot completely replace the BIW since the fixture is performing better than BIW in some respects and failing to conform to the requirements in others. The possible reason for the fixture failing to meet the requirements in the few aspects has been explored. As future work, it was proposed to explore into stiffness varying mechanisms (spring mechanisms) that could alter the stiffness requirements on the fixture as per the cockpit used for testing. It was also suggested to look for alternatives to Aluflex which would provide better stiffness at the connection points. Further, it was suggested to look for alternatives in the design concept which would avoid the connection part in extending too much away from the main structure thereby retaining high stiffness at the connection point.